Fracture Toughness of Zircaloy Cladding Tubes

The fracture toughness of Zircaloy-2 cladding has been estimated by means of the recently developed pin-loading (PL) tension test. Axially notched ring specimens, cut directly from different cladding (annealed, cold-worked, hydrided, and irradiated), have been tested in a way similar to that used for compact tension specimens.

The results of the PL tension tests, performed at temperatures of 293 and 573 K, revealed for actual cladding all main phenomena observed earlier for Zircaloy materials. A threshold hydrogen content of 600 to 700 wtppm, above which only brittle fracture occurred at ambient temperature, was observed for unirradiated cladding. Existence of a continuous hydride network in the cladding facilitated brittle fracture. There was no obvious influence of the hydrogen content of about 900 wtppm on the fracture toughness at 573 K. The irradiation changed the fracture toughness in accordance with its known influence on the ductility and strength of the cladding. Intensive load serrations occurred for both irradiated and unirradiated cladding during plastic deformation of the notched ring specimens at 573 K.

A maximum-load fracture toughness of about Jmax ≈ 100 kN/m, obtained for irradiated cladding at 573 K, is comparable with fracture toughness of the cold-worked unirradiated cladding and reasonably agrees with published results for pressure tube materials.

The PL tension test was shown to be an effective method for evaluating the fracture toughness of actual cladding after hydriding or irradiation.